Abstract

The inhibitory receptor PD-1 constrains Type 1 Diabetes (T1D) in the non-obese diabetic (NOD) mouse. However, how PD-1 influences diabetogenic CD4⁺ T cells during natural diabetes is not fully understood. To address this question we developed a novel model to investigate antigen-specific CD4⁺ T cells under physiological conditions in vivo. We transferred a low number of naïve CD4⁺ T cells from the BDC2.5 mouse into prediabetic NOD mice to mimic a physiological precursor frequency and allowed the cells to become primed by endogenous autoantigen. Transferred BDC2.5 T cells became activated, differentiated into T-bet⁺ IFNγ-producing cells, and infiltrated the pancreas. In this model, loss of PD-1, but not PD-L1, on the antigen-specific CD4⁺ T cell resulted in increased cell numbers in the spleen, pancreas-draining lymph node and pancreas. PD-1-deficiency also increased expression of the chemokine receptor CXCR3. Lastly, histological data showed that a loss of PD-1 caused BDC2.5 cells to penetrate deep into the islet core, resulting in conversion from peri-insulitis to destructive insulitis. These data support a model by which PD-1 regulates islet-reactive CD4⁺ T cells in a cell intrinsic manner by suppressing proliferation, inhibiting infiltration of the pancreas, and limiting diabetes.